1. Field of the Invention
The present invention relates to a device for proving a connection between two metal elements so as to electrically insulate the two elements, which are generally substantially tubular in shape.
2. Description of the Prior Art
In the field of petroleum exploration and exploitation, electromagnetic transmissions are often used when drilling a bore, requiring the use of an antenna comprising two tubular parts which are mechanically joined to one another but electrically insulated. It is therefore necessary to use a connector which provides electrical insulation but which is also resistant to twisting, bending, traction and compression, depending on the stresses to which the tubular elements of a drill string, a string of production tubes or a production test drill string might be subjected.
Document U.S. Pat. No. 5,163,714 describes a connector which can fulfill this function but its mechanical strength is limited, in particular by the strength of the epoxy resin used for bonding and by the reduced thicknesses of the male and female components. Furthermore, the technical solution chosen requires the connector to be of a considerable length, which does not render its use particularly easy in a bore, nor does it facilitate the method of manufacture thereof. At the same time, in view of the fact that the resin must be capable of withstanding a higher temperature, i.e. in excess of 130xc2x0 C., it is necessary to use a very expensive resin and one which is very delicate to work with.
The present invention provides a solution to the problem of the prior art, in particular one which is less expensive to make, requires a smaller connector length and has a mechanical strength which can be more readily optimized.
Accordingly, the invention relates to a device for providing a connection between two metal parts. The device is a first element with a female, conical surface and a second element having a male, conical surface. At least one of the two surfaces is coated with a thin layer of an electrically insulating material. The two elements are inserted one inside the other so that they can be mechanically joined.
The second element may be coated with the thin layer, this layer having a controlled surface state and possibly being modified.
The layer may be of a thickness ranging between 0.1 and 0.5 mm and preferably between 0.2 and 0.4 mm and may be made from a ceramic type material.
Seals may be placed substantially at the two ends of the thin layer in order to prevent penetration by any fluid between the two conical surfaces.
The incline of the conical surface may have an angle ranging between 1 and 2xc2x0 and preferably between 1.3 and 1.5xc2x0.
A third element may be joined to the second element and may come into contact with the first element by means of at least one electrically insulating ring.
The ring may have seals to provide a tight contact between the first element and the third element.
A thin layer of electrical insulation material over at least a part of the surfaces which are in contact with the ends of the first and third element may be provided.
The invention also relates to an application of forming a dipole of an antenna for transmitting or receiving electromagnetic waves.
By preference, the invention forms a dipole in a drill string, a production test drill string or casing tubes or tubing.